/*
    This file is part of Sylvan.
    Copyright (C) 2008-2018 Cute Chess authors
    Copyright (C) 2019 Wilbert Lee

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Sylvan.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef SPRT_H
#define SPRT_H

/*!
 * \brief A Sequential Probability Ratio Test
 *
 * The Sprt class implements a Sequential Probability Ratio Test (SPRT) that
 * can be used as a termination criterion for stopping a match between two
 * players when the Elo difference is known to be outside of the specified
 * interval.
 *
 * \sa http://en.wikipedia.org/wiki/Sequential_probability_ratio_test
 */
class LIB_EXPORT Sprt
{
public:
    /*! The result of the test. */
    enum Result
    {
        Continue,	//!< Continue monitoring
        AcceptH0,	//!< Accept null hypothesis H0
        AcceptH1	//!< Accept alternative hypothesis H1
    };

    /*! The result of a chess game. */
    enum GameResult
    {
        NoResult,	//!< Game ended with no result
        Win,		//!< First player won
        Loss,		//!< First player lost
        Draw		//!< Game was drawn
    };

    /*! The status of the test. */
    struct Status
    {
        Result result;	//!< Test result
        double llr;	//!< Log-likelihood ratio
        double lBound;	//!< Lower bound
        double uBound;	//!< Upper bound
    };

    /*! Creates a new uninitialized Sprt object. */
    Sprt();

    /*!
         * Returns true if the SPRT is uninitialized; otherwise
         * returns false.
         */
    bool isNull() const;

    /*!
         * Initializes the SPRT.
         *
         * \a elo0 is the Elo difference between player A and
         * player B for H0 and \a elo1 for H1.
         *
         * \a alpha is the maximum probability for a type I error and
         * \a beta for a type II error outside interval [elo0, elo1].
         */
    void initialize(double elo0, double elo1,
                    double alpha, double beta);
    /*! Returns the current status of the test. */
    Status status() const;
    /*!
         * Updates the test with \a result.
         *
         * After calling this function, status() should be called to
         * check if H0 or H1 can be accepted.
         */
    void addGameResult(GameResult result);

private:
    double m_elo0;
    double m_elo1;
    double m_alpha;
    double m_beta;
    int m_wins;
    int m_losses;
    int m_draws;
};

#endif // SPRT_H
